Rare words

and then again there is the whole group of words, where the negative is still a frequently used word, but the positive is hardly ever used or very rarely.

sorry, as it has to be expected, no good examples come to mind …

ahhh…

uncanny < === > canny?
impertinent < == > pertinent?
intransigent < == > transigent??

that kind of thing …

Funny, because I was thinking of Asomov at the mention of sesquicentennial.

indubitably and dubitably
unconscionable and conscionable
underwhelmed and whelmed
discombobulated and combobulated

a few german words come to mind:

ungehobelt <> gehobelt (ungehobelte Person) - literally transalted an unplaned person (as in unrefined) but there is no planed person
unwirsch <> wirsch

thats an interesting one … there’s underwhelmed and overwhelmed … but as you mention no whelmed (does whelmed even exist?)

canny?

Entirely cromulent in the NE of England around Tyneside, canny lad.

antipathy (negative) → pathy (neutral) → sympathy (for the Devil)

I’m not sure if all these actually had positives:

disgruntled
ruthless
gormless
inept

Inept → Adept
Ruthful means “full of sorrow” (I sure haven’t seen it used with any regularity)

I have seen just ruth used. Not sure if that was a backformation or not.

The OED to the rescue!

whelm: To cover completely with water or other fluid so as to ruin or destroy; to submerge, drown; occasionally to sink (a boat). [most recent citation 1888]

gruntle: To grumble, murmur, complain. (The dis- prefix in “disgruntled” is an intensifier.) [most recent citation 1876]

ruth: The quality of being compassionate; the feeling of sorrow for another; compassion, pity. [most recent citation 2005]

gome: Sense, wit, tact. Alternate spelling “gom”, “gawm”. “Gormless” was originally spelled “gawmless”. [most recent citation 1877, although that was in a dictionary]

apt: Natural tendency. Use as a noun was rare, derived from the adjective “apt”. [most recent citation c1400]

The non-negated forms are all perfectly valid words. To be fair, though, “transigent” is uncommon and is even omitted from some dictionaries. Google Ngram shows its usage hitting a peak in 1960 and again in 1998 for some strange reason, but its usage never exceeded 0.000000277%.

Affray is also an offense in some US jurisdictions. Including mine:
Statutes & Constitution :View Statutes : Title XLVI : Chapter 870

It’s interesting that those were the first examples. With the first two pairs, the non-negated form still exists as a common word, but they have diverged semantically - they are not semantic negations. A question can be impertinent but pertinent; it’s uncanny how canny she is.

Huh? I hear “pertinent” more often than “impertinent.” (As in “how is that pertinent to the discussion?”) Google ngram seems to agree:

Link to chart

And I think the term you’re looking for is “unpaired words”:

That actually got used quite a bit here in Ohio in the 1960-70s as all the cities settled right after the War of 1812 became 150 years old. It has tapered off, of course.

The terms “ace”,”deuce”, “trey” are familiar, but did you know there are terms for the four, five and six on a die also? They are, respectively, “cater”, “cinque”, “sice”.

There’s a form of counting of sheep in the north of England that may well be a last relic of the Cumbric/proto-Welsh

I see a couple of my favorites on that list of unpaired words, couth and wieldy.

Yes, I misrembered